Custom Monocular Calibration for Enhanced Eye-Tracking Accuracy

The standard calibration of a commercial research-grade eye tracker is based on the assumption that the user has functional binocular vision and coordination between their eyes. Under this assumption, the user can accurately fixate on the calibration targets with both eyes, enabling an accurate and effective calibration. However, this assumption does not hold when binocular visual dysfunctions, such as vergence insufficiency, strabismus, or amblyopia, are present. In these cases, while the dominant eye may accurately fixate on the target, the non-dominant or skewed eye may experience suppression, and its visual axis will not align with the fixation target. As a result, even if the standard built-in calibration procedure appears to succeed algorithmically, it will be implicitly biased by the deviation of the non-viewing eye.In this study, we present a custom monocular calibration method aimed at improving eye-tracking accuracy beyond the limitations of standard built-in calibration. This approach is specifically designed for individuals with binocular vision disorders who are unfit for traditional binocular calibration procedures. We collected data using a Head Mounted Display (HMD) using a binocular eye-tracker embedded, from five healthy participants and two individuals with binocular disorders. Results from healthy participants demonstrate a slight yet significant improvement in accuracy, confirming the approach’s suitability for general use. More interestingly, of participants with binocular visual dysfunctions the approach is effective in correcting for calibration errors resulting from the deviated eye, thus restoring the accuracy of the measured gaze direction.Clinical relevance— This approach provides a viable alternative for individuals with binocular vision disorders who are partially able or unable to complete standard binocular calibration. In fact, the proposed calibration method effectively corrects gaze errors caused by the deviated eye, enabling reliable assessment of oculomotor function, paving the way to the development of valuable diagnostic aids for clinical use.